The present invention relates to a centering device provided in an optical disc player for centering an optical disc, and more particularly to a centering device for a double-sided optical disc.
There is a certain type of optical disc which comprises two discs adhered to each other at the back thereof so that the thus assembled disc has a double recording surface, namely side A and side B. Once the assembled disc is set on a turntable of a disc player, the double side can be continuously played so that the user need not bother to flip over the disc.
However, when adhering the two discs, center holes thereof may not always accurately coincide with each other. In order to correct the deviation of the assembled disc on the turntable, a centering device is provided. The centering device has a pair of centering mechanisms, each for one of the sides A and B, and one of the mechanisms is selectively operated depending on the side to be played.
Referring to FIG. 10, a conventional centering device for centering a double-sided disc 50 comprising a lower side A disc 50a and an upper side B disc 50b is housed in a holder 31. The centering device comprises a lower portion for centering the side A disc 50a and an upper portion for centering the side B disc 50b.
The lower portion of the centering device has a hollow turntable 20 on which the disc 50 is set. The turntable 20 is fixedly mounted on a spindle shaft 21. A centering hub 22 with which the hole of the side A disc 51a engages is vertically slidably mounted on the spindle shaft 21 inside the turntable 20. A spring 23 is provided between the bottom surface of the turntable 20 and the lower end of the centering hub 22, thereby urging the centering hub 22 upward. A stopper 24 is provided on the spindle shaft 21 so as to restrict the sliding movement of the center hub 22.
The upper portion of the centering device has a clamper 30 which cooperates with the turntable 20 to clasp the disc 50 therebetween. A shaft 32 is vertically slidably mounted in the holder 31. An upper end portion of the shaft 32 projects out of the holder 31 so as to be actuated by a changeover arm 35 driven by a driving means (not shown). On the other end of the shaft 32 is fixed a centering hub 33 which is adapted to engage with the center hole of the side B disc 50b. A spring 34 having a smaller force than the spring 23 is provided between the clamper 30 and the centering hub 33, thereby urging the centering hub 33 downward.
When playing the side A disc 50a, the changeover arm 35 is disengaged from the disc as shown in FIG. 10. When the disc 50 is clamped on the turntable 20 by the clamper 30, the centering hubs 22 and 33 are pushed toward each other by the springs 23 and 34, respectively. Since the spring 23 has a larger force than the spring 34, the centering hub 22 pushes the centering hub 33, and fits in the center hole of the side A disc 50a. Thus the disc 50 is so positioned that the disc 50a is centered. Hence the side A of the disc 50 can be played.
When playing the side B of the disc 50, the changeover arm 35 is operated to push down the shaft 32, thereby pushing down the centering hub 33 as shown in FIG. 11. The centering hub 33 accordingly forces the centering hub 22 downward against the urging of the spring 23 so that the hub 22 is disengaged from the hole of the disc 50a. As the shaft 32 is further depressed, the centering hub 33 engages with the center hole of the disc 50b. As a result, the disc 50b is accurately positioned, enabling to play the side B of the disc 50.
The conventional centering device thus requires not only two centering hubs for the two recorded surfaces, but also a changeover means for selecting one of the centering hubs, such as the changeover arm in the above described example, so that the construction thereof is complicated. In addition, the disc can be played only after the hub is selected, thereby taking time to start playing.